In a power grid, power stations of significant power outputs are connected to higher-level power-control systems. Primarily, nuclear power plants, coal-fired power plants, gas-turbine power plants, hydroelectric power plants, that is, so-called large-scale power plants are interconnected.
Photovoltaic installations or, e.g., smaller combined heat and power stations deliver significantly less power in comparison with the mentioned power plants, so that the installations are not connected directly to a control system also due to their large number. The technical complexity of such a connection to a control system would be high, and the costs would be high. In this connection, refer to the following publications:    1. Mauch, K.: Power Electronic Interfaces for DER. First International Conference on the Integrated of RE and DER, Dec. 1-3, 2004, Brussels.    2. Jahn, J.; Reekers, J.; Meinhardt, M.: Decentralized Power Generation: Further Development from Pure Power Feeding to an Intelligent System, NEuK 2006.    3. Meinhardt, M.: Future Power-grid-related Linking of Photovoltaic Installations, Hannover, Apr. 24, 2006.
Photovoltaic installations deliver power outputs in the kW range, that is, significantly below the power output of large-scale power plants. Due to the rising number of such installations, feeding electrical energy from photovoltaic installations represents an increasing control problem for energy control systems. Predictions for energy contributions from these installations cannot be made precisely, because the generation of energy is dependent, for example, on solar radiation or general weather influences. Large-scale power plants, in particular, base-load power stations, can rarely react to greatly changing conditions. Therefore, a need exists for a simplified control system for the feeding of electrical power into a grid by a plurality of relatively low power output installations such as photovoltaic installations. For example, if base-load power stations are shut down, then starting them up again takes a relatively long amount of time. It is known that feeding power from photovoltaic installations has great variability. It can happen, for example, that there is no need for photovoltaic power in a power grid outside of peak times. Indeed, electrical storage devices, in particular, accumulators, are often used in photovoltaic installations as buffers, but this procedure is relatively expensive and the buffer capacities are limited. On the other hand, unused solar energy is undesirable, because it significantly reduces the cost efficiency of an installation.
Furthermore, photovoltaic installations and other installations for generating renewable power, such as small wind turbines, are positioned far away from each other.